Among conventional hermetic compressors, there is a hermetic compressor that is provided with an oil supply passage configured for communication between a cylindrical surface of an eccentric shaft and a cylindrical surface of a main shaft for the purpose of using a crankshaft having small shaft diameters and an increased amount of eccentricity (refer to, for example, PTL 1).
A description is provided of the conventional hermetic compressor described in PTL 1.
FIG. 13 is a longitudinal sectional view of the conventional hermetic compressor described in PTL 1. FIG. 14 is a top plan view of a crankshaft of the conventional hermetic compressor. FIG. 15 is a sectional view of the crankshaft of the conventional hermetic compressor.
In FIGS. 13, 14 and 15, lubricating oil 902 is stored at an inner bottom of hermetic container 901. Compressor body 903 is formed of electric motor element 906 that includes stator 904 and rotor 905 and compression element 907 disposed above electric motor element 906. Compressor body 903 is supported by suspension springs 908 and is accommodated in hermetic container 901.
Compression element 907 is formed of, for example, crankshaft 909, cylinder block 910, piston 911, and connecting rod 912.
Crankshaft 909 is formed of main shaft 913, flange 914, and eccentric shaft 915. Flange 914 is positioned at an upper end of main shaft 913 to connect main shaft 913 and eccentric shaft 915. Eccentric shaft 915 is formed eccentrically to main shaft 913 and extends upward from flange 914. Crankshaft 909 is equipped with oil supply mechanism 916 extending between a lower end and an upper end of crankshaft 909.
Oil supply mechanism 916 is formed of spiral groove 916a formed in cylindrical surface 913a of main shaft 913 and oil supply passage 917 configured for communication between an upper part of cylindrical surface 913a of main shaft 913 and cylindrical surface 915a of eccentric shaft 915.
Cylinder block 910 includes substantially cylindrical cylinder bore 918 and bearing 919 rotatably supporting main shaft 913.
Piston 911 is inserted in cylinder bore 918 so as to slidably reciprocate. Piston 911 defines compression chamber 921 in combination with valve plate 920 disposed at an end of cylinder bore 918. Piston 911 is connected to eccentric shaft 915 by connecting rod 912.
Operation and workings of the conventional hermetic compressor thus configured are described hereinafter.
As electric motor element 906 is energized, a magnetic field is generated to stator 904, thereby causing rotor 905 to rotate together with crankshaft 909. In association with rotation of main shaft 913, eccentric shaft 915 rotates eccentrically. This eccentric rotation is converted via connecting rod 912 to reciprocating motion of piston 911 in cylinder bore 918. In this way, refrigerant gas inside hermetic container 901 is sucked into compression chamber 921 for compression.
The lower end of crankshaft 909 is immersed in lubricating oil 902. Through the rotation of crankshaft 909, lubricating oil 902 passes along spiral groove 916a to be supplied to the upper part of main shaft 913 and is then supplied to eccentric shaft 915 through oil supply passage 917 for lubrication of a sliding part.
For the purpose of reducing its shaft diameters and increasing an amount of eccentricity, crankshaft 909 of the hermetic compressor has, as shown in FIG. 14, oil supply passage 917 configured for the communication between cylindrical surface 915a of eccentric shaft 915 and the upper part of cylindrical surface 913a of main shaft 913. Center line X of oil supply passage 917 is included in plane B that does not intersect axis Y of main shaft 913, but is rotated through angle α relative to plane P defined by axis Y of main shaft 913 and axis Z of eccentric shaft 915. In this way, reduction in oil supply capacity is minimized, and suitable wall thicknesses are ensured.
However, in the structure of the conventional hermetic compressor, reducing respective diameters of main shaft 913 and eccentric shaft 915 of crankshaft 909 for reduction of mechanical losses of bearing 919 and connecting rod 912 results in the sum of respective radii of main shaft 913 and eccentric shaft 915 being smaller than the amount of eccentricity, that is, no overlap between main shaft 913 and eccentric shaft 915. In this case, angle α becomes small, and openings of oil supply passage 917 at main shaft 913 and eccentric shaft 915 are disposed in a region of a load of bearing 919 and a region of a load of connecting rod 912, respectively. Consequently, bearing strength reduces.
Moreover, shaft wall thicknesses esp1 and esp2 of FIG. 15 reduce, thereby reducing mechanical strength of crankshaft 909. Increase in thickness of flange 914 can lead to improvement of the shaft wall thicknesses but problematically causes increase in total length of crankshaft 909 and increase in total height of the hermetic compressor.